v The primary objective of the Tetramer Core is to produce Class I MHC-peptide tetramers for use by the investigators in this Program Project. This technology, pioneered in the laboratories of Davis and McMichael, is now established as a highly useful approach in studies of cell mediated immune responses to pathogens. This core facility will directly support Projects 1, 2 and 3. Class I MHC-peptide tetramers will be used to detect and sort virus-specific CD8+ T cells. With these reagents, CD8+ T cells that are specific for Epstein Barr virus (EBV), Cytomegalovirus, Influenza virus, Yellow Fever virus, and Vaccinia virus can be quantified and characterized in clinical specimens and experimental systems. This core facility will provide cost-effective, high quality reagents to investigators. We will prioritize production based on considerations including MHC Class I allele frequencies in study populations, and the identification of novel optimal peptide epitopes and their restricting elements. The experience that has been accrued by this laboratory in the production of reagents over the past seven years will allow us to extend production to additional Class I MHC alleles, and to easily include different peptide epitopes as required by Program Project investigators. This core facility has a proven track record of tight quality control, and the timely production of Class I MHC- peptide tetramers greatly enhancing the ability of Program Project investigators to isolate, enumerate and characterize virus-specific CD8+ T cells.